The congregation begins in mid-September, when the first bulls arrive, hauling out on the stony beaches and, almost immediately, starting to fight. These are not minor tussles. They can be bloody battles during which noses are ripped, skin is flayed, and eyeballs end up on the ground. Stakes are high: Only a third of these males will win the chance to breed, a small number considering that they're all loaded with testosterone and equally driven to pass on their genes. Size is definitely a factor here. Bulls can tip the scales at four tons, the weight of a large SUV, and the most colossal males tend to dominate. These turf wars also feature much displaying with that improbable nose, including bellowing with it, puffing it out, and, in general, showing it off.

Scientists refer to the triumphant males as beachmasters—each will control a harem that can range in size from 20 females on the low end to larger conclaves of 300, and in extreme cases, to supersize harems of more than 1,000. When the females arrive in early October and settle down—first to have their pups, then to suckle them, and then, about three weeks after they've given birth, to mate again—part of the beachmaster's job is to protect his females from the unwanted attentions of marauding males. In larger harems a few runners-up find their place around the fringe, but the vast number of vanquished males are left on the sidelines, frustrated and still aggressive. This means more fighting.

"It's definitely not Disneyland out there," says Mike Fedak, a biologist with the U.K.'s National Environment Research Council Sea Mammal Group. "There are significant risks to this whole harem business." This is true not only for seals, but also for humans. As scientists move among the harems, they're careful not to get caught between a beachmaster and his rivals. "You really have to watch yourself," Fedak says. "They can move with amazing agility for animals with no arms or legs."

By late November the party is winding down and the adult seals, which haven't eaten during this time, have lost up to half their body weight. The pups, meanwhile, have gained about ten pounds a day during the three weeks they've fed on their mothers' rich milk. As a female prepares to return to sea, she mates, then weans her pup abruptly, leaving it to its own devices. And then she's gone, pregnant with the pup that she'll deliver next year on these same shores.